This application is based on Japanese Patent Applications No. 2001-92350 filed on Mar. 28, 2001, No. 2001-98078 filed on Mar. 30, 2001, No. 2001-285280 filed on Sep. 19, 2001, and No. 2002-13119 filed on Jan. 22, 2002 the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a variable valve timing apparatus for varying an opening/closing timing of an intake valve or an exhaust valve of an internal combustion engine.
2. Description of Related Art
A variable timing mechanism is disclosed in JP-A No. 9-324613. This variable timing mechanism employs a lock pin capable of locking a rotor at a position (hereinafter referred to as intermediate phase position) where the rotor rotates a predetermined angle to an advance angle side from the largest delay angle position. When an engine starts, this lock pin is engaged with a lock depressed portion to lock the rotor at the intermediate phase position to thereby provide a given valve timing suitable for starting the engine. Further, after the engine starts, the lock pin is disengaged from the lock depressed portion to enable the rotor to rotate to a delay angle side further than the intermediate phase position, whereby the vale timing can be varied to both of the delay angle side and the advance angle side.
However, the lock pin disclosed in the abovementioned publication has a structure in which when the engine starts, hydraulic pressure is applied to the lock pin to disengage the lock pin from the lock depressed portion. Once the lock pin is disengaged from the lock depression, the lock pin does not act during a normal operation. For this reason, it is necessary to lock the lock pin at the intermediate phase position so that the rotor does not rotate to the largest delay angle position during an idling operation. However, when the number of revolution is low, in particular, when the temperature of the hydraulic oil is high, there is the case where the hydraulic pressure is decreased to make it impossible to secure the hydraulic pressure required to lock the rotor at the intermediate phase position.
Further, there is a problem that when an engine stall occurs, the rotor moves to and stops at the largest delay angle position to make it difficult to start the engine again.
The present invention has been made in view of the above circumstances, and it is the object of the present invention to provide a variable valve timing apparatus capable of securing a good startability of an internal combustion engine and expanding the variable range of a valve timing.
According to one aspect of the present invention, the variable valve timing apparatus has the first member for restricting a rotor""s rotating to a part of operating range and the second member for locking the rotor at an intermediate position. As a result, the first member can prevent the rotor from reaching an undesirable range. On the other hand, the releasing of restriction of the rotation of the rotor by the first member can allow the rotor to rotate to the restricted range. For this reason, it is possible to realize a suitable valve timing as required. Further, since the second member fixes the rotor at the intermediate position, it can prevent the undesirable rotation of the rotor.
The intermediate position may be, for example, a position suitable for the starting of an engine. The range restricted by the first member may be a range on a delay angle side with respect to the intermediate position. As a result, it is possible to surely produce a valve timing suitable for the starting of the engine.
According to another aspect of the present invention, the variable valve timing apparatus has a rotor rotation restricting unit having a restricting pin for restricting the rotation of the rotor. This restricting pin moves according to a pressure difference between the first control chamber and the second control chamber. The restricting pin can restrict the rotation of the rotor and can prevent the rotor from reaching an undesirable range. On the other hand, the releasing of restriction of the rotation of the rotor can rotate the rotor within a wide range. As a result, it is possible to realize a suitable valve timing as required. Further, it is possible to control the restricting pin according to the pressure balance between the first control chamber and the second control chamber. For example, it is possible to lock the restricting pin at a restricting position.
According to still another aspect of the present invention, the variable valve timing apparatus has a lock pin for locking the rotor and a delay angle restricting pin for preventing the rotor from rotating from the intermediate position to a delay angle side. This delay angle restricting pin is urged by a spring to a restricting position and is moved by hydraulic pressure to a restriction releasing position. Therefore, the delay angle restricting pin is moved to the restricting position when the hydraulic pressure is decreased. Even when an engine speed is low and the hydraulic pressure is low, or even when an oil temperature is high and thus the hydraulic pressure becomes low, it is possible to surely keep the delay angle restricting pin at the restricting position.
According to still another aspect of the present invention, the variable valve timing apparatus has a restricting pin for restricting the rotational range of the rotor. The restricting pin is moved to the restricting position by a spring. The restricting pin is supplied with the hydraulic pressure by an exclusive oil passage provided independently of an oil passage for supplying the hydraulic pressure for rotating the rotor, thereby being moved to the restriction releasing position. The exclusive oil passage makes it possible to control the restricting pin without affecting the hydraulic pressure for rotating the rotor. For example, even when the engine speed is low and the hydraulic pressure is low, or even when the oil temperature is high and thus the hydraulic pressure becomes low, it is possible to surely keep the delay angle restricting pin at the restricting position.
According to still another aspect of the present invention, the variable valve timing apparatus has a pin which can move to three positions. The pin allows the rotor to freely rotate at the first position and restricts the rotational range of the rotor at the second position and locks the rotation of the rotor at the third position. Therefore, it is possible to selectively realize the restricting of rotation of the rotor and the locking of the rotor by only one pin.